New user calibration check for TT bike

[bmswalla]

Hi, I've just received and installed my PowerPod this past weekend and would like to make sure my calibration data looks ok! My sense is that the power reading are on the high side, but not sure... This is for a TT bike and I did the calibration in the areo position.

Thank you!!!
Brian

[bmswalla]

In case it's helpful, I attached a few images showing my cockpit and how I mounted the PP. I reversed the combo/TT mount to put the PP a little lower since I have my Garmin watch mounted out in front on a custom watch mount, and I thought this may be important to prevent an effect on the PP from the watch.

Does this look ok?

Thanks!!

[Velocomp]

Your PowerPod is angled too high; the word "PowerPod" should be approximately level to the ground.

You can rotate the PP to the "other" stop on the mount. That likely will improve things sufficiently.

[bmswalla]

Hi John,

Thank you. I wondered about that...

I assume I should perform another calibration ride after adjusting the angle?

I'll report back after next ride!

Brian

[bmswalla]

Forgot to ask - does the PP need to be that low, or would I be ok with the mount in its normal orientation?

Alternatively, I'm also thinking about mounting the PP to the side so I can fit a hydration bottle between the bars, as I saw may be an option in another post. Are there any concerns with this approach?

In either case I'll make sure to get the PP more level as you recommend.

Thanks again!

[Velocomp]

I would mount your PP close to the handlebars, to minimize the possibility of vibration.

Mounting it to the side is also OK, but again, close to the handlebars to minimize vibration.

[bmswalla]

Hi again,

I mounted the PP out to the side of my TT bars, closer to the handlebars (about an inch forward), and rotated the PP back (instead of forwards) to the stop in the mount. This allowed the writing to be parallel to the ground as recommended.

Attached is my new calibration ride for profile #2, and a short ~6 mile ride I did afterwards, which was a pretty hard effort. It was windy again today.

Please let me know how everything looks!

Thank you!

[Velocomp]

This one looks great!

Have fun...

[bmswalla]

Great, thanks!!

One more question: if I mount the water bottle between the bars do I need to recalibrate due to potential wind effects from the bottle? It's not in front of the PO , but would be parallel to the side.

Thanks again for the great support!

[Velocomp]

It shouldn't have a significant effect but if you want post a ride file with the bottle and I'll take a look.

[bmswalla]

Hi John,

Here's a ride form this morning with the bottle mounted. It was pretty calm and not much wind (first time in a while). Also quite a bit colder than usual if that makes any difference -- today was 38-39F, previous rides have been 50-55F.

Thanks again for taking a look!
Brian

[Velocomp]

I looked at your ride file.

I do apologize but, unfortunately, the first time I looked at your ride file I did not look carefully at your CdA and Crr figures.

On a TT bike, both numbers should be much lower than yours.

As I explored your problem I just discovered a bug in Isaac for Mac that does not allow proper setting of TT bike CdA.

THIS TT CDA BUG DOES NOT AFFECT ISAAC FOR WINDOWS.

I manually set your CdA and Crr for your TT bike:

1) I adjusted your CdA and Crr to TT values (about 0.256 and .0042 respectively)

2) I applied the corrected profile to your ride file

3) I tweaked the ride file with the Check Calibration feature

These changes bring down your numbers considerably, but hey...you're riding a TT bike!

Load the profile into your bike and you should be all set for your future rides.

[bmswalla]

Hi again John,

Back again for another ride check from you, if you would be so kind!

I changed my wheels (less aero, I think, and not performance tires) and added some gear behind the seat (bottle cages, tool bag, light, CO2 cart etc), so thought maybe I should do a new OAB calibration to see if anything would be different (not sure if this was really necessary...). PP mount is the same and unchanged from before, and I tried to start with the same values from profile you manually edited previously. For some reason the PP didn't go into calibration mode with my new profile, so I trimmed the ride file afterwards and used check calibration on the OAB section (5/8 file). It was windy during the ride (around 10mph I think).

Today I did another longer OAB ride (5/11 file), and I noticed that the power readings seemed to fluctuate a lot relative to my perceived exertion -- on downhills power seemed low, and on uphills it seemed too high. Average seemed about right though. So afterwards I again used the check calibration on the 5/11 ride, which recommended changes to aero and wind scaling factors.

Could you take a look and let me know what you think of these rides and profiles? I'm trying to finalize this profile before starting deeper training. The calibrated values I ended up with are different from the profile you tweaked for me above by quite a bit, which I didn't expect.

Thank you in advance for the help!!!

[bmswalla]

Hi John,

I saw in another thread there's a firmware bug affecting Power for TT users -- would this have any impact on my results?

I haven't been able to ride since 5-11 so not yet able to test the newly tweaked profile I made based on check calibration of 5/11 ride file above. I am hoping the power reading will be more consistent.

Still would value your feedback on my new ride files above and the modified profile using my 5/11 data.

Thank you!

[Velocomp]

Your ride file looks good. Please post your next ride...

[bmswalla]

Ok, was able to get out this morning. Ride file attached.

This time was a little different, at first, I felt like the power readings were again low on descents and high on climbs, relative to my perceived effort, which I tried to keep more or less constant. But in the latter half of the ride everything seemed better.

Then, when I merged my garmin/strava data to get the GPS track, I saw that the speed data in the garmin file is really weird for a while, then gets better (see pic below). This section of scattered data seems to correlate with when I experienced the variable power, and then it seems to go away about when I felt the power was more correct. It looks like the PP data is not affected though.

Do you know what is going on and is this something I should worry about? My sensor is a combo/magnet on the rear chainstay (not the GSC-10 that I know can cause problems -- not sure of the make will have to go look).


Thanks again for your help, John!!
Brian

[cheoherrera]

Your PowerPod is angled too high; the word "PowerPod" should be approximately level to the ground.

You can rotate the PP to the "other" stop on the mount. That likely will improve things sufficiently.

question, does this angle issue apply to the regular Ibike Newton as well? i havent upgraded to the PowerPod yet and i am having the same issue, readings are too high... i just raced IM 70.3 Gulf Coast and i had a Avg Watts of 365W for the entire 56 mile ride (i did pushed it and rode in 2:23, but still....)

[Velocomp]

Just replied to your other post.

[bmswalla]

I just checked and have the Bontrager Ant+ speed/cadence sensor. I put a fresh battery in it just before installing the PP a couple weeks ago.

Any thoughts on my files above?

Thanks!!

[bmswalla]

Hi John,

Any feedback on this?

1. How does the 5/16 ride file look to you?

2. Is there a reason the PP would give higher than expected power on climbs and less on descents?

3. Any thoughts on what is going on with the Garmin speed data, and is there any effect on the PP and power calcs?

I'm planning to ride again tomorrow with the same profile unless I hear different from you tonight.

Thanks!

[Velocomp]

Your most recent ride file looks PERFECT!

When GPS data is unreliable you'll get "noise" in the speed signal. This is about your Garmin, not about PP.